The present invention pertains to a double-walled pipe with integrated heating capability for an aircraft or spacecraft and a method for manufacturing a double-walled pipe of this type.
Although applicable to various pipe systems for any kind of aircraft or spacecraft or the like, the present invention and the problem on which it is based will be explained in greater detail with reference to water pipes of commercial aircraft. In principle, however, the present invention may also be utilized in other pipe systems that are configured for transportation of various fluids like oil, fuel, water or the like. Further, the present invention may be used in various parts of aircraft, like, for example, aircrafts floors, wings, cargo bays, etc., in particular, in the context of ice protection applications.
In contemporary commercial aircraft a plurality of water pipes are used for applications like waste water transportation, cargo drainage, or humidifier piping. These pipes are often formed from stainless steel or titanium and are connected by welded elbows and T-pieces or similar elements. However, the temperature of the air around aircraft may drop significantly below the freezing point during operation in high altitudes. In order to prevent water pipes from freezing during flight, water conduits are typically heated and/or drained of any fluid. Heating may, for example, be provided by a linear tape heater. In this case, a linear electrical heating tape may be attached to one side of the pipes. In addition, the heater and/or the pipes may be surrounded by electrical and/or thermal insulation means. In order to transfer heat from a heater to the pipe walls more efficiently, a heating layer may be provided that fully surrounds the outer surface of the pipes. In this case, the entire pipe surface may be heated and power consumption may be reduced.
Document DE 10 2010 010 929 A1 discloses, for example, a self-heating water conduit segment made from metal with an integrated heating device. The heating device is a semiconductor heating device comprising an inner conductor being surrounded by a semiconductor layer, which in turn is surrounded by an outer conductor. The inner conductor hereby serves as an inner pipe for water transportation.
Document DE 20 2005 004 602 U1 discloses a heated flexible plastic hose that includes an extruded inner plastic sleeve surrounded by a layer of a conductive polymer with a positive temperature coefficient (PTC) for heating of the inner sleeve. The conductive layer itself is surrounded by an outer plastic sleeve that is sprayed on the conductive layer.
In general, any weight reduction per pipe can have significant impact on aircraft load and, in consequence, fuel consumption. In addition, it is desirable to provide a means of heating that is as uniform and efficient as possible with minimal installation and/or production effort. 3D printing provides extraordinary design freedom and hence it is widely used for manufacturing with multiple applications in engineering, construction, industrial design, automotive industries, and aerospace industries. Amongst various advantages, it offers the possibility to manufacture complex hollow rigid structures in one piece that are much more cumbersome to produce with conventional manufacturing methods. Conventional methods often do not allow to produce hollow objects in an integral way at all, but require to assemble these from a number of individual subcomponents.